Machines such as, for example, dozers, loaders, excavators, motor graders, and other types of heavy machinery use one or more hydraulic actuators to accomplish a variety of tasks. These actuators are fluidly connected to a pump on the machine that provides pressurized fluid to chambers within the actuators. A valve arrangement is typically fluidly connected between the pump and at least one of the actuators to control a flow rate and direction of pressurized fluid to and from the chambers of the actuator.
The valve arrangement may include independent metering valves (IMVs) that are independently actuated to allow pressurized hydraulic fluid to flow from the pump to the actuator chambers. The amount of the hydraulic flow to each actuator chamber can be controlled by changing the displacement of a valve spool in each IMV. Each valve spool has a series of metering slots which control flows of the hydraulic fluid in the valve arrangement, including a flow from the pump to the actuator and a flow from the actuator to a tank. When the actuator is a hydraulic cylinder, these flows are commonly referred to as pump-to-cylinder flow and cylinder-to-tank, respectively.
The manufacture and assembly of the IMVs may affect the performance of the valve components such that each IMV may perform differently from the others. As a result, the valve components may not operate predictably and the performance of the hydraulic actuator may be degraded.
One method of controlling flow through a valve arrangement fluidly connected between a pump and an actuator is described in U.S. Pat. No. 6,397,655 (“the '655 patent”) issued to Stephenson. The '655 patent describes a method of calibrating an inlet valve or an outlet valve connected to an actuator chamber. The inlet valve controls the amount of flow supplied to the actuator chamber, and the outlet valve controls the amount of flow exiting the actuator chamber. To calibrate the inlet valve, the outlet valve is closed while current to actuate the inlet valve increases, thereby increasing the pressure in the actuator chamber. A valve opening current level for the inlet valve is determined when a rate of increase in pressure in the actuator chamber exceeds a predetermined threshold. To calibrate the outlet valve, the inlet valve is opened so that the pressure in the actuator chamber increases. The inlet valve is then closed, and the current to actuate the outlet valve is increased. A valve opening current level for the outlet valve is determined when a magnitude of the rate of decrease in pressure in the actuator chamber exceeds a predetermined threshold. The calibration ensures that the difference between the valve opening current level for the inlet or outlet valve and an initial current level for the respective valve differs by at least a desired margin.
The calibration method of the '655 patent determines a predefined initial current level that is initially applied to the valve. This initial current level is a desired amount less than the current level at which the valve begins to open. The initial current level supplied to the inlet or outlet valve is adjusted only when there exists a difference between the measured valve opening current and the initial current level. The '655 patent also requires pressure sensors at the respective cylinder ports, which requires a sensor at each cylinder port. This increases the number of sensors, thereby increasing the complexity of the calibration process. Furthermore, the '655 patent measures the valve opening current level when the rate of pressure change reaches a predetermined threshold, but does not determine whether the rate of pressure change remains above the predetermined threshold for a predetermined period of time. Therefore, the calibration method of the '655 patent may determine the valve opening current level prematurely if there is an error in measuring the rate of pressure change due to signal noise or leakage through the inlet or outlet valve.
The disclosed system is directed to overcoming one or more of the problems set forth above.